1. Field of the Invention
The present invention relates to a tape cassette for accommodating a magnetic tape and more particularly to the miniaturization of in addition, the construction of a detecting mechanism of a device corresponding to the tape cassette.
2. Description of the Related Art
In an 8 mm tape cassette, a detecting opening for preventing an erroneous erasure of the recorded content is provided in a rear corner of a tape cassette case. A user slides a cover which opens or closes the detecting opening and as a result, a device decides whether or not the recorded content can be erased. In the device, a sensor for deciding whether the detecting opening is opened or closed is disposed immediately below the detecting opening. Thus, the information of the tape cassette is decided by the information obtained by the sensor. A similar detecting opening is provided in a tape cassette of a VHS or a DAT.
The tape cassette accommodates a detecting optical path for detecting the leading and rear end of a tape. In the 8 mm video tape cassette, an insertion opening for inserting a detector of an emission side is provided in a triangular space enclosed by right and left tape reels and the inner wall of a tape loading pocket. A detecting optical path is interposed between the insertion opening and an optical path window formed on the right and left side walls of the case of the tape cassette. In adopting an optical method for detecting the ends of the tape to be carried out by this construction, it is normal that a rotation locking member for locking the rotation of the tape reel is disposed in a space, enclosed by both reels, disposed in the rear of the tape cassette. In detecting the tape ends by another method, a rotation locking member for locking the tape reel can be disposed in a space enclosed by a tape path disposed in the front of the tape cassette and the side walls thereof. This construction is effective for preventing the loosening of the tape disposed inside the tape cassette because the reel is urged toward the rear of the tape cassette. The former method is adopted in the tape cassette of a VHS or an 8 mm tape cassette. The latter is adopted in the tape cassette of office use, 1/2 inch digital (D2 format). The tape cassette of a VHS, Beta-max system, and 8 mm video system are known and the tape cassette of D2 format is described in page 358 through 374 of a SMPTE Journal, March 1986.
The position of a distinguishing member is important for applying tape cassettes of a large size and a smaller size to the same tape deck. For example, if the distinguishing member is disposed in the same position as that of the 8 mm video tape cassette currently used, namely, if the distinguishing member is provided in a rear corner of the case of the tape cassette, it is necessary to provide a detecting tool for deciding the change-over state of the distinguishing member suitable for both tape cassettes of a large size and a smaller size or move one detecting tool according to tape cassettes of a large size and a smaller size. Regardless of whether one detecting tool or two detecting tools are provided, the tape deck has unavoidably a complicated internal construction.
As disclosed in Japanese Utility Model Laid-Open Publication No. 62-888, it is possible to dispose the distinguishing member in a space enclosed by left and right tape reels. But this construction does not allow a detecting optical path to be provided in an appropriate position. In particular, in a tape cassette of the small size, the detecting optical path is unavoidably disposed in a tape loading pocket. In this case, it is impossible to provide an opening for insertion a detector of the emission section of a magnetic recording/reproducing device inside the tape cassette case.
In making the tape cassette compatible, it is necessary to simplify the internal construction of a tape deck. As a result, some parts of the tape cassette are disposed at inappropriate positions. On the contrary, in order to dispose parts appropriately in the tape cassette, the internal construction of the tape deck is unavoidably complicated.
As another method, the leading and rear ends of the tape are detected by the leading end of a magnetic tape fed out from the tape cassette. In this case, it is necessary to make the leading end of the magnetic tape longer than that of the tape cassette of the VHS system and the 8 mm video system which detects the leading and rear ends of the tape inside the tape cassette. As a result, the leading end of the magnetic tape is caught by a cylinder in loading the tape in the tape cassette, which may damage a cylinder head. In addition, since a mechanism for detecting the tape ends is disposed outside the tape cassette, the device becomes unavoidably large and complicated.